PS Days - Evian 24-26.1.2001 / MV 1

The SPL : a High-Power Superconducting H– Linac at CERN

MotivationsMotivations ApplicationsApplications Design featuresDesign features ImprovementsImprovements ConclusionsConclusions

M. Vretenar for the SPL Study Group: B. Autin, K. Bongardt, R. Cappi, F. Caspers, E. Chiaveri, R. Garoby, F. Gerigk, H. Haseroth, C. Hill, A. Krusche, D. Kuchler, M. Lindroos, A. Lombardi, R. Losito, M. Poehler, H. Ravn, M. Sanmarti, H. Schönauer, M. Silari, J. Tückmantel, M. Vretenar

SPLSPL = Superconducting Proton Linac

PS Days - Evian 24-26.1.2001 / MV 2

The SPL - Motivations

to improve the quantity and quality of the proton beams provided by the PS Complex advantages for the LHC

production of intense secondary beams for the Neutrino Factory and other users

to modernise the injectors with standard equipment to use the LEP Superconducting RF system

The LEP SC-RF system:288 SC cavities in 72 cryostats(812 meters!), 44 klystrons

PS Days - Evian 24-26.1.2001 / MV 3

The SPL - Applications

High-brightness injector for the PS (factor 3 in beam brightness, higher intensity for all users)

Proton driver for a Neutrino Factory (with accumulator / compressor rings in the ISR, 4 MW beam power)

Driver for a second generation radioactive beam facility (SuperISOLDE)

PS Days - Evian 24-26.1.2001 / MV 4

The SPL - Main parameters (1)

All details inthe SPL Yellow Report

(Conceptual Design of the SPL)CERN 2000-012

H-

RFQ1 chop. RFQ2RFQ1 chop. RFQ2 RFQ1 chop. RFQ2DTL CCDTL RFQ1 chop. RFQ2 0.52 0.7 0.8 LEP-II dump

Source Low Energy section DTL Superconducting section

45 keV 7 MeV 120 MeV 1.08 GeV 2.2 GeV

3 MeV 18MeV 237MeV 389MeV

13m 78m 334m 345m

PS / Isolde

Stretching andcollimation line

Accumulator Ring

773 m

PS Days - Evian 24-26.1.2001 / MV 5

Main parameters (2)

2.2 GeV: LEP cavities (=1) are efficient for W>1GeV Reduced space charge tune shift in the PS for injection energies > 1.4 GeV (present PSB) Efficient pion production for the Neutrino Factory for W > 2 GeV

Pulsed Injector Linacs for protons and H-

1

10

100

1000

10000

10 100 1000 10000

Energy [MeV]

Ave

rage

Cur

rent

[ A

]

CERN-SPLJHP

LANL

SNS

ESS

RAL

BNL

FNAL

INR

CERN

ANLIHEP1

IHEP

IHEPKEK

MV 16.5.00

75 Hz : for intense beams, a high rep. rate reduces charge per pulse (possible only with linacs!), limit given by power efficiency

LEP cavities TTF

11 mA : optimum distribution of klystrons, same current as LEP2

PS Days - Evian 24-26.1.2001 / MV 6

The SPL - Main Design Features

H- source,25 mA16.5% duty

Fast chopper (2ns)

Cell-Coupled DTL, 352 MHz

new SC cavities at =0.52, 0.7, 0.8

RF system:all at 352 MHz,combination of tetrodesand LEP klystrons

Careful beam dynamicsdesign, large apertures to avoid halo formation and beam losses(50M particles + mismatch OK)

H-

RFQ1 chop. RFQ2RFQ1 chop. RFQ2 RFQ1 chop. RFQ2DTL CCDTL RFQ1 chop. RFQ2 0.52 0.7 0.8 LEP-II dump

Source Low Energy section DTL Superconducting section

45 keV 7 MeV 120 MeV 1.08 GeV 2.2 GeV

3 MeV 18MeV 237MeV 389MeV

13m 78m 334m 345m

PS / Isolde

Stretching andcollimation line

Accumulator Ring

Section Inputenergy

Outputenergy

Numberof cavities

Peak RFPower

Number ofklystrons

Numberof tetrodes

Length

(MeV) (MeV) (MW) (m)

Source, LEBT – 0.045 – – – – 3

RFQ1 0.045 2 1 0.3 1 – 2

Chopper line 2 2 2 – – 2 6

RFQ2 2 7 1 0.5 1 – 5

DTL 7 120 100 8.7 11 – 78

SC – reduced 120 1080 122 10.6 12 74 334

SC – LEP 1080 2200 108 12.3 18 – 345

Debunching 2200 2200 8 – 1 – 26

TOTAL 334 32.4 44 76 799

PS Days - Evian 24-26.1.2001 / MV 7

The Chopper

.80 cm2.2 ms

5.60 cm13.3 ms

.80 cm14.2 ns

1.30 cm22.7 ns

{

5 bunches

linac macropulse

linac micropulse

accumulator bucket

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Travelling wave electrostatic deflector, meander line to match beam and wave velocity Used to create gaps in the linac bunch distribution between accumulator buckets Needs very short rise/fall times (2 ns !) to avoid partially deflected bunches Development of pulser

PS Days - Evian 24-26.1.2001 / MV 8

The Drift Tube Linac

7 - 18 MeV: “classic” Alvarez linac 18 - 120 MeV: Cell Coupled DTL concept

The quadrupoles are taken out of the drift tubesShort (2-gaps) DTL cavities are connected by off-axis coupling cavities.

Advantages of the CCDTL: Higher shunt impedance (less power) Simple access and alignment for the quadrupoles Relaxed mechanical tolerancies (lower cost) One klystron per string of cavities FODO focusing is maintained

PS Days - Evian 24-26.1.2001 / MV 9

The Superconducting Linac

To standardise construction,* 3 families of cavities optimised for different betas* cavities are grouped in cryostats* =0.8 cavities in LEP cryostats

PS Days - Evian 24-26.1.2001 / MV 10

The SC cavities for < 1

The =0.7 4-cell prototype

CERN technique of Nb/Cu sputteringfor =0.7, =0.8 cavities (352 MHz):• excellent thermal and mechanical stability (very important for pulsed systems)• lower material cost, large apertures, released tolerances, 4.5 K operation with Q = 109

Bulk Nb or mixed technique for =0.52 (one 100 kW tetrode per cavity)

0.1

1

10

0 2 4 6 8 10 12

Eacc [MV/m]

Q/1

09

0.8 single cellLEP0.7 4-cells0.8 5-cells

PS Days - Evian 24-26.1.2001 / MV 11

Pulsing of the SC cavities

The LEP RF is CW, pulsing (75 Hz, 2.2 ms) a SC system is an additional complication. Problems:• low power efficiency due to long cavity filling times• high sensitivity to vibrations:

“small” mechanical vibrations (external, or Lorentz force) large detuning (high Q!) large V and errors

solutions (under study): appropriate feedback loops, reduce number of cavities per RF unit, debunching to minimise W at ring injection.

PS Days - Evian 24-26.1.2001 / MV 12

SPL Design - Beam Dynamics

Goal: beam loss below 1 W/m to avoid activation of components (0.5 nA/m @ 2 GeV)

Beam size evolution in the SC linac (aperture 200 mm)

matched case

strongly mismatched case

100%

rms

rms

100%

Careful beam dynamics design to avoid halo formation:minimise effects of mismatched beameliminate sources of mismatchsimulations with 50M particles (1/6 of bunch !)

Conclusion:no loss or halo seen in thesimulations

PS Days - Evian 24-26.1.2001 / MV 13

Layout on the CERN site

Linac + klystron galleryLinac + klystron galleryparallel to the fence of parallel to the fence of Meyrin site (Route Meyrin site (Route Gregory) Gregory) Economic trench excavation Geological advantages (tunnel on“molasse”, no underground water) Minimum impact on the environment (empty field) Simple connection to PS & ISR via existing tunnels Use some of the old ISR infrastructure (electricity, cooling)

PS Days - Evian 24-26.1.2001 / MV 14

SPL Layout - Tunnels

* “Cut and cover” technique* >8 meters of earth for shielding* tunnel on the molasse* linac slope 1.4%

PS Days - Evian 24-26.1.2001 / MV 15

SPL Layout - connections to PS, ISR

* 2 bunching/debunching sections and 230m drift to increase beam length to 180 ps and to reduce energy jitter coming from SC cavity vibrations* only 100m of line before connecting to the existing tunnel network* easy connection to ISOLDE (old and new)

PS Days - Evian 24-26.1.2001 / MV 16

Improvements to the present design

with respect to the present reference design (Yellow Report), some points can be improved, with the aim of:- reducing the power consumption (40 MW for 4 MW beam power, i.e. 10% conversion efficiency)- reducing the cost of the machine

DESIGN IMPROVEMENTS New design with repetition frequency down to 50 Hz, increased current and/or pulse length Re-optimised layout of SC section Dare to reduce the apertures to reduce cost of the machine ? Design a room-temperature alternative structure for the expensive =0.52 SC section

HARDWARE TEST IN 2001 Test of LEP klystrons in pulsed mode Test of SC cavities in pulsed mode Construction and tests of a chopper pulser prototype High Power test of a CW DTL model, collaboration with CEA/Saclay

PS Days - Evian 24-26.1.2001 / MV 17

Conclusions

43% of the cavities, 60% of the cryostats and all the klystrons of LEP can be used for a 2.2 GeV pulsed H– Linac.

A 2.2 GeV, 4 MW beam power linac at CERN would allow the PS to produce beams of high intensity and quality, and makes possible the production of muons for a Neutrino Factory and of other secondary beams.

The design of the linac has been outlined This machine fits nicely on the CERN site

PS Days - Evian 24-26.1.2001 / MV 18

H-

RFQ1 chop. RFQ2RFQ1 chop. RFQ2 RFQ1 chop. RFQ2DTL CCDTL RFQ1 chop. RFQ2 0.52 0.7 0.8 LEP-II dump

Source Low Energy section DTL Superconducting section

45 keV 7 MeV 120 MeV 1.08 GeV 2.2 GeV

3 MeV 18MeV 237MeV 389MeV

13m 78m 334m 345m

PS / Isolde

Stretching andcollimation line

Accumulator Ring